usual place for tumble dryers to short is at the rear of the machine where the cables emerge to the heating elements. This happened on an Indesit we had. The cabling/elements are contained under a housing on the rear of the unit. The cables emerge from the main body of the unit through a hole which unfortunately has next to nothing in the way of insulation around it- the cables are pretty tight and general movement of the machine causes the cable insulation to wear and you then get a nice short to ground and off goes your trip. You can repair it with tape/ heatshrink sleeving, replace the wiring but it will happen again a few months later.